-if difference in size is less than 15%, extensive substitution is possible,if not, this is limited

Substituion cations have the same charge and about the same size. (olivine - fayalite (fe) and forsterite (mg))

charge balance is maintained by coupling one substiution that increases the charge with another that reduces the charge - PLAGIOCLASE

What it Omission solid solution?

E.g. Pyrrhotite

Fe1-XS (X= 0 -0.02)

3Fe2+ <--> 2Fe3+ + ____

Charge balance is maintained when ions of different charge substitute for each other by leaving structuralsites vacant or unfilled

What is interstitial substitution?

E.g. Beryl

A variation of couples substitution in which charge balance in maintained by placing ions in sites that are normally vacant.

___ +Si4+ <--> Al3++(K+,Rb+,Cs+)

Crytal growth process
which crystals are the most prominant on a crystal and why?

- Adding a new materical to a face leaves many bonds unsatisfied

- Having an EDGE availabile allows new material to be added without as many unsatisfied bonds.

- Growth on a SCREW DISLOCATION (a crystal defect)allows the face to grow in a continuous spiral

The slowest growing crystal faces are the most likely to be prominent on a crystal. The fastest growing faces {111} have a net charge and high surface energy as opposed to the (100) faces which are uncharged and grow slow. The fastest growing however grow at a speed which results in their dissapearence.

Why are their only 8 abundant minerals that make up the earths crust?

- primordial metarial accumulated to form the earth - prepresented by chondritic meteorites whose major minerology includes olivine and pyroxine.

- less abundant minerals are only known from meteorites because their chemiscal and physical conditions needed for formation are not found on earth

what are the three types of defects that influence properties of a crystal